The performance of a dry sampler, with an impregnated denuder in series with a glass fibre filter, using di-n-butylamine (DBA) for airborne isocyanates (200ml min⁻¹) is investigated and compared with an impinger flask with a glass fibre filter in series (1 l min⁻¹). An exposure chamber containing 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and 2,4- and 2,6-toluene diisocyanate (TDI) in the concentration range of 5–205 μg m⁻³ [0.7–33 p.p.b.; relative humidity (RH) 50%], generated by gas- and liquid-phase permeation, was used for the investigation. The precision for the dry sampling for five series with eight samplers were in the range of 2.0–6.1% with an average of 3.8%. During 120-min sampling (n = 4), no breakthrough was observed when analysing samplers in series. Sixty-four exposed samplers were analysed after storage for 0, 7, 14, and 21 days. No breakdown of isocyanate derivatives was observed. Twenty-eight samplers in groups of eight were collecting isocyanates during 0.5–32h. Virtually linear relationships were obtained with regard to sampling time and collected isocyanates with correlation coefficients in the range of 0.998–0.999 with the intercept close to the origin. Pre- or post-exposure to ambient air did not affect the result. Dry sampling (n = 48) with impinger-filter sampling (n = 48) of thermal decomposition product of polyurethane polymers, at RH 20, 40, 60, and 90%, was compared for 11 isocyanate compounds. The ratio between the different isocyanates collected with dry samplers and impinger-filter samplers was in the range of 0.80–1.14 for RH = 20%, 0.8–1.25 for RH = 40%, 0.76–1.4 for RH = 60%, and 0.72–3.7 for RH = 90%. Taking into account experimental errors, it seems clear that isocyanic acid DBA derivatives are found at higher levels in the dry samples compared with impinger-filter samplers at elevated humidity. The dry sampling using DBA as the reagent enables easy and robust sampling without the need of field extraction.

An advanced design of a denuder impactor (DI) sampler has been developed for characterization of possible airborne isocyanate exposure in different particle size fractions. The sampler is equipped with 12 different parallel denuder tubes, 4 impaction stages with the cut-off values (d₅₀) of: 9.5, 4, 2.5 and 1 µm, and an end filter that collects particles < 1 µm. All collecting parts were impregnated with di-n-butylamine DBA as the reagent in a mixture with acetic acid. The performance of the DI sampler was studied on a standard atmosphere containing gas and particulate isocyanates. The isocyanate atmosphere was generated by liquid permeation of 2,4-, 2,6-Toluene Diisocyanate (TDI), 1,6-Hexamethylene Diisocyanate (HDI) and Isophorone Diisocyanate (IPDI). 4,4’-Methylene Diphenyl Diisocyanate (MDI) particles were generated by heating of technical MDI and condensing the mixture of gas and particle-borne MDI in an atmosphere containing mixed salt particles. The study was performed in a 0.85 m³ environmental chamber with stainless steel walls. With the advancement of the DI sampler it is now possible to collect isocyanate particle samples for up to 320min. The performance of the DI sampler is essentially unaffected by the humidity. The DI sampler and the ASSET™ EZ4-NCO sampler (Sigma-Aldrich/Supelco, Bellefonte, PA, USA) gave similar results. Sample losses within the DI sampler are low. In the environmental chamber it was observed that the particle distribution may be affected by the humidity and ageing. A scanning mobility particle sizer (SMPS) was used to separate a flow of selected fractions containing MDI particles from mixed MDI and salt particles. The particle-size distribution had a maximum at about 300nm, but later in the environmental chamber 1 µm dominated. The distribution was very different as compared to with only NaCl or MDI present. The biological relevance for studying isocyanate nano particles is significant as these have the possibility to reach the lower airways where allergic reactions may occur. SMPS and isocyanate air sampling can be used for the investigation of isocyanate nano particles.

We report the development of proton transfer reaction-mass spectrometry (PTR-MS) methodology for on-line monitoring, using a direct reading instrument, of several typical gas phase isocyanates, including isocyanic acid (ICA), ethyl isocyanate (EIC), phenyl isocyanate (PhI), hexamethylene diisocyanate (HDI) and toluene diisocyanate (TDI). In the study, ICA and MIC were generated by thermal degradation of urea and 1,3-dimethylurea, respectively, while the other isocyanates were generated by liquid and gas permeation techniques. Comparative, reference measurements were made by sampling isocyanate atmosphere using impinger flasks containing the reagent di-n-butyl amine (DBA) then determining the resulting DBA derivatives by liquid chromatography (LC)-MS/MS. Reproducible measurements were obtained, with a <10 % drift in PTR-MS responses during a 12 month period. Further, there were linear correlations (R2>0.99) between the data acquired by the PTR-MS technique and air sampling followed by LC-MS/MS for all tested isocyanates in the concentration range 2-100 ppb, with a PTR-MS detection limits in the low ppb range. For all isocyanates except EIC, BIC, HDI and IPDI, the protonated molecular ions were the most abundant ions in the PTR mass spectra. Overall, the results show that the developed method enables sensitive, time-resolved measurements of airborne isocyanates to be acquired over several weeks.

In some industries, the temperature and the humidity will vary greatly between different work places, such as outdoor work in arctic or tropical climates. There is therefore a need to test respirator filters at conditions that simulate conditions that are relevant for the industries that they are used in. Filter cartridges were exposed to controlled atmospheres of varying isocyanate concentration, air humidity, and temperature in an exposure chamber. For isocyanic acid (ICA) and methyl isocyanate (MIC), the exposure concentrations were between 100 and 200 p.p.b., monitored using a proton transfer reaction mass spectrometer. ICA and MIC were generated by continuous thermal degradation of urea and dimethylurea. The breakthrough was studied by collecting air samples at the outlet of the filter cartridges using impinger flasks or dry samplers with di-n-butylamine as derivatization reagent for isocyanates followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. For hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI), the exposure concentrations were between 4 and 20 p.p.b. and were generated by wet membrane permeation. To reveal the profile of adsorption in different layers of the respirator filters, representative samples from each of the layers were hydrolyzed. The hydrolysis products hexamethylene diamine and isophorone diamine were determined after derivatization with pentafluoropropionic anhydride (PFPA) followed by LC-MS/MS analysis. The two filter types studied efficiently absorbed both ICA and MIC. There was no trend of impaired performance throughout 48-h exposure tests. Even when the filters were exposed to high concentrations (similar to 200 p.p.b.) of ICA and MIC for 96 h, the isocyanates were efficiently absorbed with only a limited breakthrough. The majority of the HDI and IPDI (> 90%) were absorbed in the top layers of the absorbant, but HDI and IPDI penetrated farther down into the respirator filters during 120 h of exposure as compared to 16 h exposure.

This study has examined the distribution patterns between gas phase and particle phase of some chemical compounds produced in fires. It has also addressed the question of the distribution of individual particle-associated species between the different size-ranges of particles. The chemical compounds studied and discussed in this paper are polycyclic aromatic hydrocarbons (PAHs), and isocyanates. The steady-state tube furnace, ISO/TS 19700, was chosen as the physical fire model in order to study the production of particles from different types of fire exposure, that is, oxidative pyrolysis, well-ventilated flaming fires and under-ventilated flaming post-flashover fires. Two materials were chosen for investigation, a polyvinyl chloride (PVC) carpet and a wood board. The particle production from the two materials investigated varied concerning both the amounts produced and the particle size distributions. The analysis of PAHs showed that volatile PAHs were generally dominant. However, when the toxicity of the individual species was taken into account, the relative importance between volatile and particle-associated PAHs shifted the dominance to particle-bound PAH for both materials. The substantial degradation in the tests of the low polyurethane content of the PVC carpet, and the (4,4-methylenediphenyl diisocyanate)-based binder in the wood board resulted in no or very small amount of quantifiable diisocyanates.